Field of the Invention
The present invention relates to a vibration element, a method for manufacturing the same, and a vibration-type driving device, and in particular to a vibration element having a substrate and a piezoelectric element fixed thereon, a method for manufacturing the same, and a vibration-type driving device including the vibration element.
Description of the Related Art
In related art, a vibration-type driving device (a vibration wave actuator, for example) typically includes a piezoelectric element that functions as a vibration source of a vibration element (also referred to as a vibrator). Examples of the piezoelectric element include a single plate-like piezoelectric element and a more recent multi-layer piezoelectric element having multiple piezoelectric layers and electrode layers stacked alternately as taught in Japanese Patent Application Laid-Open No. 2004-304887.
FIG. 7 is an outline perspective view of a linear, vibration-type driving device 20 (an ultrasonic actuator) according to Japanese Patent Application Laid-Open No. 2004-304887.
The linear, vibration-type driving device 20 includes a vibration element 21 and a linear slider 26 that is a driven element in pressure contact therewith.
The vibration element 21 has a multi-layer piezoelectric element 23 and a vibration plate 22. The multi-layer piezoelectric element 23 has piezoelectric layers and electrode layers bonded alternately with an adhesive.
The vibration plate 22 made of metal has a plate portion formed into a rectangular shape and two protruding portions 24 each formed into a protrusive shape on the top surface of the plate portion. The protruding portions 24 each have a contact portion 25 on the top surface thereof. The contact (friction) portions 25, which are members brought into direct contact with the linear slider 26 that is a driven element, are made of alumina (aluminum oxide) that is abrasion resistant ceramics.
The shape of the vibration element 21 of the linear, vibration-type actuator 20 is determined so that the resonance frequencies in two flexural vibration modes, which are a primary flexural vibration mode in the long-axis direction and a secondary flexural vibration mode in the short-axis direction, approximately coincide with each other. Input of predetermined high-frequency voltages having phases different from each other by approximately π/2 causes the vibration element 21 to be excited, which excites circular movement or elliptical movement of the protruding portions 24.
The circular movement or elliptical movement generates a force to move the linear slider 26 in pressure contact with the vibration element 21 relative to the vibration element 21 with the frictional force. The relative movement force allows the linear slider 26 to be driven in a linear reciprocating manner in the direction shown by the arrow.
Such a multi-layer piezoelectric element 23 can be produced as follows. First, green sheets to be piezoelectric layers are formed from a piezoelectric powder material and an organic binder by such a method as the doctor blade method, and an electrode paste material is printed on predetermined positions on the green sheets to produce electrode layers.
Subsequently, a predetermined number of such green sheets are stacked in a planar state and pressurized to form a laminate. Thereafter, the piezoelectric layers and the electrode layers are integrated by being sintered together, then subjected to poling, and finally subjected to machining to be finished into a predetermined size.
Furthermore, Japanese Patent No. 2842448 proposes a piezoelectric/electroresistive actuator having an integrated multilayered structure formed by sequentially stacking an electrode material and a piezoelectric material into a laminate on at least one surface of a substrate and integrating the stacked materials by heat treatment.
Moreover, Japanese Patent Application Laid-Open No. 2011-254569 proposes a vibration element in which a piezoelectric element having piezoelectric layers and electrode layers is fixed onto a substrate and which causes the substrate to vibrate by vibration energy of the piezoelectric element.
The vibration element includes a bonding layer that is a ceramic layer containing glass powder between the piezoelectric element and the substrate. The piezoelectric element is fixed to the substrate with the bonding layer therebetween by sintering.
In the vibration element 21 of the vibration-type driving device of the related art illustrated in FIG. 7 described above, the multi-layer piezoelectric element 23 and the vibration plate (hereinafter referred to as a substrate) 22 made of metal are bonded with a resin adhesive. The resin adhesive, however, is softer than the piezoelectric element and the metal, which makes the vibration damping of the vibration element larger and, particularly when the temperature of the resin is higher, lowers the efficiency of the vibration-type driving device.
Furthermore, as the vibration-type driving device is made smaller, influences of the variation in the thickness of the bonding layer of the adhesive and of the positional accuracy of the bonding on the performance of the small vibration-type driving device become larger and the variation in the performance of the small vibration-type driving device thus becomes larger.
Moreover, the method for manufacturing multi-layer piezoelectric elements of the related art requires a high amount of equipment investment for such manufacturing equipment as a machine for forming green sheets from the piezoelectric powder material, a laminating press, and a processing machine, which contributes to an increase in the manufacturing cost.
An attempt is thus made to directly fix (bond) the multi-layer piezoelectric element onto the substrate without providing a bonding layer of an adhesive simultaneously with production of the multi-layer piezoelectric element as taught in Japanese Patent No. 2842448 of the related art mentioned above.
The ceramic substrate and the electrode layers made of noble metal, however, are less chemically reactive and lower in bonding strength. The piezoelectric element thus has such problems that the piezoelectric element is likely to be separated from the ceramic substrate during sintering and is also separated by vibration of the actuator.
A vibration element produced as follows as taught in Japanese Patent Application No. 2011-254569 of the related art mentioned above is thus proposed. The vibration element is produced by providing the bonding layer containing glass powder between the piezoelectric element and the ceramic substrate, sintering the piezoelectric element and the substrate together, and melting the glass powder to bond the piezoelectric element and the substrate to each other. With such a structure, however, there still are problems that separation and cracks are caused near the boundary between the bonding layer and the piezoelectric element and that the expected performance of the vibration element cannot be provided. Furthermore, owing to high sintering temperatures, it is difficult to use 100% by weight of silver as an electrode material.